Polyethylene terephthalate (PET) is increasingly used in the outer layer of oriented films, in direct co-extrusion, to give the film the stiffness, heat resistance, and gloss. The PET provides, in combination with a barrier film, like PE-PA-EVOH-PA-PE film, the high stiffness, temperature resistance, puncture resistance, and high barrier properties needed to package food, with the security of a high oxygen barrier and excellent puncture resistance. To produce such films, the PET has to be coextruded, using an extrudable tie layer that can provide the interlayer adhesion between the PET and the polyolefin or barrier layer.
Typically, the structures, such as PET/tie/PE/Tie/PA/tie/PE; PET/tie/ionomer or EAA/tie/PA/EVOH/PA/tie/PE; or PET/tie/PE/Tie/PA/EVOH/tie/PE are often extruded into films ranging from 35 to 150 microns. Some conventional tie-layer solutions include maleic anhydride modified ethylene methylacrylate polymers, and maleic anhydride modified ethylene vinyl acetate polymers. The tie layer requirements have been becoming more demanding, requiring higher adhesion properties. However these current tie-layer materials are often disadvantageous because of negative taste and odor properties and/or insufficient thermal stability at high processing temperatures (≥225° C.). Thus, there is a need for new film compositions that contain tie-layers that have improved adhesion to polyesters, good high temperature processibility, and low taste and odor levels.
U.S. Pat. No. 7,635,509 discloses multilayer film webs having a layer of an oxygen-permeable composition that is a blend of the following: i) an organic acid or organic acid salt; ii) a copolymer of a) ethylene, b) an C3 to C8 α, β-ethylenically unsaturated carboxylic acid, and optionally c) an alkyl acrylate or alkyl methacrylate comonomer; and iii) at least one additional ethylene-containing polymer selected from the group consisting of ethylene homopolymers and ethylene copolymers, other than ethylene acid copolymers and ionomers. Greater than 70% of the total acid moieties of (i) plus (ii) are neutralized to the corresponding metal salts.
U.S. Pat. No. 5,139,805 discloses a multi-ply, heat-shrinkable film that has a surface layer for contact with a cooked or processed meat product. The film surface layer is formed of an ethylene-ethyl acrylate-maleic anhydride copolymer, or a mixture of the ethylene-ethyl acrylate-maleic anhydride copolymer and a polyolefin. The content of ethyl acrylate component in the surface layer is 2 to 20%, by weight, and the content of maleic anhydride component is 1 to 5%, by weight.
International Publication WO 2012/037180 discloses a multilayer film structure, and more particularly a formable, high vapor barrier, multilayer film structure. The film structure comprises at least the following four layers: a) a core layer comprising a polyvinylidene chloride resin, b) a first tie layer, c) a second tie layer, and d) a first copolyester outer layer that has an intrinsic viscosity of 0.4 dl/g to 0.7 dl/g. Optionally, the multilayer film structure comprises a second outer layer comprising one or more copolyester resins. The multilayer film structure may optionally have one or more inner layer and/or one or more additional tie layer between each of the outer/inner layers and the first and second tie layers.
EP Patent 1049751B1 discloses a polyethylene-based adhesive composition which contain as little as five weight percent, and up to 35 weight percent of an acid-grafted metallocene polyethylene. The adhesive composition is disclosed as having superior peel strength to comparable compositions containing an acid grafted, non-metallocene and EVA or EMA polyethylene. Compositions, where the acid-grafted metallocene polyethylene component is based on a metallocene polyethylene, having a melt-flow ratio of less than 6.53, and an Mw/Mn of greater than the melt flow ratio less 4.63, are disclosed as good adhesive compositions.
JP2006117709A (Abstract) disclosed a polyester film suitable for the packaging use, and which is disclosed as having little “over-time change” of a physical property, and as having a low-temperature heat-sealing property. The film is formed by the inflation molding of a resin composition, comprising from 1 to 20 weight percent of an ethylene-based-copolymer (C), which is modified|denatured [carboxylic-acid-] or modified|denatured [epoxy], and 5 to 50 weight % of ethylene-polymer (B) of density 0.850-0.910 (g/cm3).
Additional compositions are disclosed in the following references: U.S. Pat. No. 4,639,398; U.S. Publication Nos. 2007275219 and 20120064269; International Publication WO 2008080111; De Gooijer, J. M., et al., Polym. Eng. Sci. 41, 86-94, 2001; Becker, P., et al., 1389-94, ANTEC 1991 (Abstract); Durgun, H, et al., Adhesion Sci. Technol., 19, 407-425, 2005 (Abstract); Becker et al., Annual Technical Conference-Society of Plastic Engineers, 1991, 49th, 1389-94 (Abstract).
However, as discussed above, there remains a need for new multilayer film configurations that contain tie-layers compositions that have improved adhesion to polyesters. These needs and others have been met by the following invention.